To meet the demand for wireless data traffic having increased since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’. The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems. In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
The Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of Things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The Internet of Everything (IoE), which is a combination of the IoT technology and the Big Data processing technology through connection with a cloud server, has emerged. As technology elements, such as “sensing technology”, “wired/wireless communication and network infrastructure”, “service interface technology”, and “Security technology” have been demanded for IoT implementation, a sensor network, a Machine-to-Machine (M2M) communication, Machine Type Communication (MTC), and so forth have been recently researched. Such an IoT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things. IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between existing Information Technology (IT) and various industrial applications.
In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as a sensor network, Machine Type Communication (MTC), and Machine-to-Machine (M2M) communication may be implemented by beamforming, MIMO, and array antennas. Application of a cloud Radio Access Network (RAN) as the above-described Big Data processing technology may also be considered to be as an example of convergence between the 5G technology and the IoT technology.
With the rapid advance of wireless communication technology, communication systems have evolved to the 4th Generation mobile communication systems represented by the LTE system. The LTE system employs several key technologies to meet the demand of increasing traffic, and Carrier Aggregation (CA) is one of such technologies. CA is a technique for use of one or more component carriers in addition to a primary component carrier to increase the data rate between a terminal (hereinafter, referred to as User Equipment or UE) and a base station (hereinafter, referred to as evolved Node B or eNB) in proportion to the number of component carriers, which is unlike the legacy communication system that uses one component carrier.
In LTE, the primary and secondary component carriers are referred to as Primary Cell (PCell) and Secondary Cell (SCell), respectively. The LTE (Release 11) supports one PCell plus up to four SCells, and the number of supportable SCells may increase in the future.
Although the LTE system is designed to operate in a frequency band that the government licenses to a mobile operator, many technical studies on the use of unlicensed bands already populated by devices operating on other technologies such as WLAN and Bluetooth are being conducted to meet the increasing traffic demand, and Licensed Assisted Access (LAA) is a promising technology enabling LTE to operate in unlicensed bands.
Independent of the LAA technology, a technology called LTE-WLAN (carrier) aggregation or integration is under discussion for simultaneous use of both the licensed LTE band and unlicensed WLAN band.
In the case of using the CA technique along with the LAA technology, it may be possible to consider a scenario where the PCell operates on a licensed band frequency while the SCell operates on an unlicensed band frequency with the LAA technology. In the case of using the CA technique along with the LTE-WLAN integration technology, it may be possible to consider a scenario where the PCell operates on a licensed band frequency while the SCell operates on an unlicensed band frequency with the WLAN technology.
Both the cases have a drawback in that using an unlicensed band as a supplementary band increases power consumption of the UE.